Spark plug



Feb. 15, 1949.

L. H. CROOK 2,461,590

SPARK PLUG Filed Dec. 9, 1943 Fatenied Feb. H5, 2949 UNITED STATESPATENT OFFICE SPARK PLUG Louis B. Crook,Washington, D. 0. ApplicationDecember 9, 1943, Serial No. 513,581

8 Claims. 1

This invention relates to spark plu s. i h radio shielded or unshielded,for internal combustion engines.

ne of the principal objects of the invention is to improve theelectrical, thermal, and mechanical features of a spark plug, thereby toincrease the overall efliciency, and enable it satisfactorily to meetthe increasing requirements of temperature and pressure conditions ofthe modern internal combustion engine.

Another important object of the invention is to provide a spark plug inwhich overheating is prevented by insulating the plug where it isdirectly subjected to the influence of the hot gases of the combustionchamber of the engine.

A further object is to provide a spark plug in which the electrodes areprotected, by suitable insulating means, from excessive heating, thuspreventing pre-ignition and prolonging the life of the electrodes.

A further object is to provide a spark plug in which injury to thedielectric of the main body of the plug, as well as the dielectric ofthe adjacent cable in the case of a shielded spark plug, by overheatingof the plug, is prevented.

A further object is to provide a spark plug which may be very small indiameter so as to be used safely in engines having high temperature andpressure requirements.

My invention accordingly consists in the features of construction andcomposition of the members and in the relative proportioning anddisposition thereof, all as more completely outlined herein.

To enable others skilled in the art fully to comprehend the underlyingfeatures of this invention and the modifications in structure andrelation contemplated thereby, drawings depicting several of the variouspossible embodiments of the invention have been annexed as part of thisdisclosure, and in such drawings like characters of reference denotecorresponding parts throughout all of the views, in which Fig. 1 is adetail view showing the barrel or outer electrode of a preferred form ofmy invention housing the inner electrode and dielectric of the plug.

Figs. 2, 3, and 4 are end views of various forms of barrel.

Figs. 5 and 6 are cross-sectional views of two forms of the invention.

This spark plug comprises a core I2 the dielectric of which may be ofinsulating material such as mica or porcelain such. as in common use inmost spark plugs and through the center of which 2 core passes oneelectrode l3 adapted to be connected in any suitable manner with thesource of electric power.

Surrounding the core i2 is a thin metal barrel which in the presentinstance comprises a tubular member l4 preferably of electrode metal, orof other suitable highly conductive material both as to heat andelectricity, which is screw threaded for a considerable distance asindicated at l5. This barrel when made of electrode metal, terminates atits lower end in a plurality of electricterminals i6 which may behomogeneous with the metal of the barrel. The barrel, however. may bemade of a non-electrode metal with the electrodes of a suitableelectrode material welded to the lower end thereof. It is advantageous,however, to avoid the use of welded joints, which tend to impede thefree fiow of heat. These terminals or electrodes i6 coact with thecenter electrode l3 in the customary manner.

Surrounding the lower part of the barrel H is a sleeve of heatinsulating material.

In assembling the parts the dielectric I2 and center electrode 13 arepositioned Within the barrel H by the usual factory methods. In themodifications shown in Figs. 3 and 4, the barrel M in Fig. 3 is providedwith four electrodes l6, and the barrel ii" in Fig. 4 is provided withone such electrode. 7

In the modification shown in Fig. 6 the heat insulating ceramic material25 is cast between a metal shell 26 and the metal barrel H of anunshielded plug, the threads IS on the barrel and hollow-shaped portionof the shell at 33 serving as lugs to hold the various members in fixedrelation to one another. In case the barrel is de sired detachable fromthe ceramic 25 the threads [5 serve as accurate screw threads forscrewing the barrel into the ceramic, and in such cases it is preferableto provide a metal lock nut as shown at 40 in Fig. 5.

The metal shell 26 in Fig. 6 serves as a means for strengthening theenclosed ceramic material, and a means for providing the screw-threadedportion at 39 to engage Withthe cylinder wall. At the same time itprovides heat radiating fins 36. The portion of the barrel exposed todirect action of the hot gases is made as small as possible in keepingwith the electrical requirements and protects as much as possible fromthe radiation and conduction of the hot gases by extending the heatinsulating material and metal shell over the outer electrodes as shownat 35 and M, respectively.

The metal extension II in Fig. 6 carries the heat toward the metal ofthe cylinder block and the heat is radiated to the atmosphere by meansof the flns 38. Thus, a very large percentage of the lower area of thenormal spark plug in contact with the hot gases, does not in thisinvention directly contact the metal of the electrodes.

In the modification in Fig. and here shown applied to a radio shieldedplug, the heat insulating material constitutes the large part of theplug. Means for lockingthebarrel ll into the shell 26 is'here shown as ascrew thread with lock nut 40. The shell is formed'as a hexnutpreferably finned for radiating purposes, and screw threaded at 89 forengagement with the cylinder block. The lower portion of this shelladjacent to the electrode points is preferably shaped or streamlined asshown at 29 to allow a smoother flow of the compressed gases and at thesame time protect as much as possible the electrodes from the direct andintense radiant heat from the hot gases.

In all cases where the heat insulation means is applied to an unshieldedspark plug a small metal rod, as indicated at A3 in Fig. 6, is insertedthrough the insulation at a point near the outer electrodes and embeddedtherein so as to ground the spark plug to the cylinder block and permitthe ready flow of the ignition current through the engine. There is nonecessity for this in a shielded plug, the return being by way of theshield of the ignition system, of which the shield of the spark plugforms a part.

The word "ceramic used herein is to be understood as embracing suchporcelains and the like which are molded and baked under hightemperature conditions and which have a high degree of heat resistanceand a coefiicient of expansion approximately the same as the adjacentmetal. While such materials, as well as mica also mentioned herein, arealso electrical insulators as well as heat insulators, that feature maybe disregarded insofar as my shieldedspark plug is concerned, forrepeated tests have proved that no current will flow from the spark plugto the engine block in a completely shielded ignition system in whichthis plug "Is especially adapted to be used, i. e., in a shielded systemas shown and described in my prior United States Patent No. 1,645,643,dated October 18, 1927. In the case of an unshielded plug, however,special means for grounding the plug to the engine block, so as toinsure the free flow of the return current through the engine-should beused, as explained above. I

It will be apparent that the heat insulating feature of my inventionconsists primarily of materially reducing the amount of metal of a sparkplug which is exposed to the direct action of the hot gases of thecombustion chamber of the engine. Where the portion of the spark plugentering the cylinder wall consists entirely of insulating material,only a small part of metal, being that of the electrodes within thefiring chamher of the spark plug, is so exposed. Where a metallic sleeveor shell surrounds the insulating material, the metal thereof is alsoexposed, but this has little effect in the way of heating up the sparkplug proper since it is insulated therefrom. Thus, protection to thespark plug as a whole is provided against excessive heating due toradiation, conduction and convection from the a hot gases as they passback and forth through the interstices of the lower portion of the plug.

While the application of my invention for heat insulating a shieldedspark plug is shown in the drawings as applied to a spark plugin whichthe shield is in the form of a cylinder which is an integral part of thespark plug proper, it will be apparent that this feature may beincorporated also in a shielded spark plug in which the shield is in theform of a cap or dome crimped or otherwise held to the body of acompleted and otherwise unshielded spark plug, such, for example, as isshown in my Canadian Patent No. 294,403, dated November 5, 1929. p

The invention is of simple and practical construction and may be easilyandinexpensively manufactured, assembled and installed withoutmodification of any of the parts of the engine itself as now in use.

Likewise, whilekeeping the dimensions of the barrel or main body of theplug more or less standard, my spark plug can be readily adapted to meetthe particular temperature requirements of difierent engines by merelyattaching to the barrel of the plug the heat insulating and radiatingmembers of appropriate types and dimensions as described above.

While the invention has been described in accordance with the preferredembodiments, it is apparent that many variations and modifications maybe resorted to without departing from the scope of equivalents withinthe purview and spirit of this invention as defined in the followingclaims.

I claim:

l. A spark plug adapted to be inserted into an engine block including acentral part with cooperatin electrodes, and a sleeve of heat insulatingmaterial between the central part and the walls of the opening in theengine block in which the plug is inserted, said sleeve projectingbeyond and partly covering said electrodes at their outer ends toprotect them from gaseous products of combustion within the engine.

2. In a spark plug for combustion engines having metal electrodes, thecombination of a metal shell externally threaded to engage the usualspark plug opening in the engine block, and means interposed between theshell and adjacent portions of the spark plug surrounding and partlyenclosing the exposed ends of the electrodes to reduce the radiation ofheat from the engine gases thereto, said means being of a heatinsulating material adapted to withstand high temperatures.

3. A spark plug as set forth in claim 2 including means providingelectrical contact with the engine through the heat insulating material.

4. In an unshielded spark plug having a barrel portion and electrodes,an exteriorly threaded metal shell to engage the threaded opening of anengine cylinder,'heat insulating material interposed between the shelland adjacent portions of the spark plug, and means providing electricalcontact of the barrel of the plug with the engine, said means consistingof a metal member embedded in the insulating material at a point nearthe outer electrodes and contacting the barrel of the plug and theshell.

5. A spark plug as set forth in claim 4 in which the metal membercontacts the barrel of the plug and the wall of the engine.

6. A spark plug especially adapted for use in shielded ignition systemscomprising, in combination, a barrel of electrically conductive materialhaving a core, an electrode therein, said barrel terminating in at leastone electrode, a ceramic member surrounding said barrel at its lowerend, the lower portion of said member being exteriorly threaded toengage the threaded opening of an QJILBOO 8 engine cylinder and thZNDDer Portion terminating in a nut for screwing the plug in and out ofthe cylinder. and a lock nut in threaded engagement with the barrel andpositioned above the said ceramic member.

7. In a spark plug having a hollow metallic body. an electrode withinthe body, a dielectric material between the electrode and the body, anda heat insulating material on the outside of the body surrounding andpartly enclosing the exposed end of said electrode and adjacent portionoi said body.

8. In a spark plug having a hollow metallic casing, an electrode withinthe casing, a. dielectric material between the electrode and the casing.an exterior-1y threaded metallic shell, and a heat insulating materialbetween the casing and the shell surrounding and partly enclosing theexposed end of said electrode and casing, said shell protecting theexposed end oi said heat insulating material.

LOUIS H. CROOK.

REFERENCES CITED The following references are of record in the file oithis patent:

